1. Field of the Invention
This invention relates to computer video display technology, and more particularly, to a method and apparatus for automatically detecting whether a video output port on a computer video display adapter is currently externally connected or disconnected. In practice, the invention can be utilized, for example, on a video display adapter having an S output port and an AV Output port to detect which one of them is currently externally connected for video transmission to the video display unit.
2. Description of Related Art
A video display adapter for a personal computer (PC) is typically included with a television (TV) function that allows the PC monitor or a TV set to display digital video programs. This kind of video display card includes two different kinds of video output ports--an S output port and an AV output port--for connection to a PC monitor or a TV set. Conventionally, the use of the S output port or the AV output port is selectively set by jumper means or through software means by the operating, system (OS) of the computer. These setting methods, however, are both inconvenient to carry out.
If the video display card is set to use the AV output port, when the S output port on the TV set is connected via a cable to the S output port on the video display card, the video signal from the video display card is almost impossible to display on the TV screen. This is because the output video signal from the S output port is coded in a non-composite format, while the output video signal from the AV output port is coded in a composite format.
One drawback to the S/AV setting by the OS is that it can be carried out only after the computer is powered on and booted up, and the video image that is displayed after power-on and prior to entering the OS cannot be changed.
One drawback to the use of jumper means to set the S/AV option is that it is quite inconvenient to carry out since it requires the user to dismantle the PC case each time the jumper setting is to be changed.